Using API to get child skus from configured composite sku

Question

I'm using the Magento API to get SKUs from an order. We have a set of "configured" items that allow selecting optional add-on products but the order API returns these items as what seems to be called a "composite" SKU which looks like: "ITEM-BASE-SKU-OPTIONAL-SKU-ONE-OPTIONAL-SKU-TWO". How do I get the "children" of a sku that looks like this? All I need is to reliably get the child strings; the lookup can be a separate call.